1. Field of the Invention
The present invention relates to a component inaccuracy correction system, and more particularly, to a correction system for correcting a resistance inaccuracy caused by an integrated circuit manufacturing process.
2. Description of the Prior Art
Integrated circuits arewidely found in day-to-day life, from watches and cellular telephones, all the way to super-computers. However, due to problems in manufacturing process controls, the characteristics of each component in an integrated circuit may deviate from the characteristics originally designed, and so the functionality of the integrated circuit may not meet the original design specifications. For example, the resistors in an integrated circuit may have inaccurate resistance values because the fabrication process is not ideal. Such process inaccuracies makes the real resistance values of all resistor components in the integrated circuit deviate from the original design values by the same ratio, i.e. the ratio of deviation from the original design value of each resistor component in the integrated circuit is the same.
To avoid the above-mentioned resistance inaccuracies, U.S. Pat. No. 5,625,316 offers an inaccuracy correction system to correct resistance inaccuracies in a wave filter. Please refer to FIG. 1. FIG. 1 is a block diagram of a prior art component inaccuracy correction system 510 used to correct resistance inaccuracies of the wavefilter 520. The wave filter 520 comprises a resistor Rf and a variable capacitor 560. The product of the two is the RC time constant that determines the bandwidth of the wave filter 520. If the resistance of Rf is affected by the integrated circuit manufacturing process and is inaccurate, the bandwidth of the wave filter 520 may deviate from the original, designed value. To keep the bandwidth fixed, the component inaccuracy correction system 510 changes the value of the capacitor 560 to compensate for inaccuracies in the resistance of Rf.
In the prior art component inaccuracy correction system 510, Vcc provides a bias voltage for the correction system 510. The resistorRref is an additional resistor installed outside of the integrated circuit, and so having a resistance that is not affected by the integrated circuit manufacturing process. The resistor Rc and the resistor Rf of the wave filter 520 are both made in the same integrated circuit manufacturing process, and so both of these resistors may suffer the same level of resistance inaccuracies. The correction system 510 further comprises a regulated generator 530 for producing a standard voltage Vbg, a reference voltage generator 540 for producing a reference voltage Vref according to the standard voltage Vbg, and an analog-to-digital converter (ADC) 550.
The working principle of the prior art component inaccuracy correction system 510 is described as follows. The regulated generator 530 generates a standard voltage Vbg, and the standard voltage Vbg is not only inputted into the reference voltage generator 540 to generate the reference voltage Vref, but is also linked to one end of the additional resistor Rref by way of the operational amplifierP to create a reference current Iref according to the voltage drop across Rref. That is, Iref=(Vccxe2x88x92Vbg)/Rref. The reference current Iref flows through the transistor T and the resistor Rc, and generates a comparison voltage Vc. As mentioned above, the resistance values of Rc and Rf of the wave filter 520 have the same level of deviation from the designed values because both are fabricated in the same integrated circuit manufacturing process. By comparing the reference voltage Vref to the comparison voltage Vc, the resistance inaccuracies of the resistorRc and the resistor Rf of the wave filter 520 can be learned. The analog-to-digital converter 550 is used to compare the reference voltage Vref to the comparison voltage Vc and to generate corresponding control signals to change the value of the variable capacitor 560 of the wave filter 520 to compensate for the the resistance inaccuracies.
A shortcoming of the component inaccuracy correction system 510 is that both Vcc and Vbg are needed to create the standard current Iref. In some electronic devices, especially in portable electronic devices, the power supplied to the integrated circuit is generated by a battery. As battery power is consumed, the bias voltage Vcc deviates from a required value. In this situation, even though the regulated generator 530 may provide a stable voltage Vbg, the standard current Iref will nevertheless be incorrect. An incorrect reference current Iref with the resistor Rc will necessarily generate an incorrect comparison voltage Vc. When the analog-to-digital converter 550 compares the incorrect comparison voltage Vc to the correct reference voltage Vref, resistance inaccuracies cannot be properly corrected.
It is therefore a primary objective of the present invention to provide a component inaccuracy correction system to solve the above-mentioned problem.
In a preferred embodiment, the present invention provides a component inaccuracy correction system for correcting component inaccuracy in an integrated circuit. This component inaccuracy is caused by the fabrication process for making the component, which may cause characteristics of the component to deviate from an original design value. The component inaccuracy correction system has a current source capable of outputting two currents with a fixed ratio, a voltage dividing circuit formed on the integrated circuit having at least an output end capable of receiving a current of the current source to create and output a divided voltage, a reference voltage generator capable of receiving another current of the current source to create and output a reference voltage, a comparison circuit electrically connected to the output end of the voltage dividing circuit for receiving the divided voltage from the voltage dividing circuit and comparing the divided voltage to the reference voltage to create a corresponding comparison signal, and a correction circuit electrically connected to the comparison circuit for correcting the component inaccuracy on the integrated circuit according to the comparison signal generated by the comparison circuit.
It is an advantage of the present invention that the component inaccuracy correction system uses a current generator to supply current respectively to an additional resistor and a set of series resistors so that the additional resistor and the series resistors generate a fixed ratio between the reference voltage and the divided voltage to prevent the component inaccuracy correction system from incorrectly correcting resistance inaccuracies due to power changes.
These and other objectives and advantages of the present invention will no doubt become obvious to those of ordinary skill in the art after having read the following detailed description of the preferred embodiment that is illustrated in the various figures and drawings.